Photodynamic therapy (PDT) is of proven efficacy for treatment of actinic keratosis (AK) and is increasingly used internationally. It involves the topical application of 5-aminolaevulinic acid cream (ALA) or its methyl ester methyl 5-aminolaevulinic acid (MAL), which is absorbed into the AK and converted into a photosensitizing compound protoporphyrin IX. When the AK is then exposed to visible light an oxygen dependent photochemical reaction is induced which results in cell death through apoptosis and necrosis.